1. Field of the Invention
Embodiments of the invention generally relate to detecting particles flowing in a fluid within a conduit.
2. Description of the Related Art
Production of particles, such as sand, concerns operators of oil/gas wells because of possible catastrophic consequences on production. In this disclosure, “sand” refers to solid particulate matter as would be found in an oil/gas well, without particular regard to its size or diameter. The production of sand may result in clogged well lines that can effectively fill in the well and halt production. Sand can also congest separator tanks, which typically connect other producing wells. When this congestion occurs, the production of all oil wells feeding into the separator tanks must be halted. Furthermore, sand production can erode flow lines, chokes, etc., and can cause a catastrophic failure or breach of the piping system.
Mechanical sand control devices such as expandable sand screens, gravel packs, etc. are designed to mitigate sand production. However, operators still need to monitor sand, so that evasive action can be taken if sand production is increasing beyond tolerable levels, due to e.g., sand screen failure. Once sand is detected, the operator may lower the drawdown to reduce the amount of produced sand. Operators often apply conservative production limits for the maximum production rates due to the serious consequences associated with undetected sand production. Thus, a large incentive exists in the industry for methods of detecting sand quickly and continuously.
A variety of methods currently exist in the oil and gas industry to detect sand production. One such method involves physically filtering a sample of produced fluids to check for solid particles. However, contamination of the separator tanks and completion equipment may occur prior to the filtering that takes place after the fluid has risen to the top of the well. Furthermore, the filtering of selected samples only detects sand at designated time intervals.
Intrusive sand erosion probes provide an alternative technology to detect sand. The probe includes a sacrificial element immersed in the flow stream. Measured changes in electrical properties as the element erodes from impinging sand particles can be used to detect sand. Disadvantages of the probe include a limited lifespan and the fact that the element must enter the pipe and obstruct part of the flow stream. Accordingly, the probe is unsuitable for downhole installation.
Another device that continuously monitors for sand production senses the vibrations caused by sand impacting the pipe in which the sand flows. The device clamps on to the pipe at a ninety degree elbow or section of the pipe where the fluid takes an abrupt turn. Consequently, the devise is unsuitable in straight or slightly bent piping networks downhole and is thereby limited to the surface environment. This technique of listening for impact vibration of the sand often requires in situ calibration by artificial injection of sand into the flow stream and can still provide false readings if the multiphase flow field is changing.
Fiber optic sensors and flowmeters already monitor parameters such as fluid sound speed, fluid velocity, pressure, and temperature. Such fiber optic based flowmeters are disclosed in the following U.S. Patents, and are hereby incorporated by reference in their entireties: U.S. Pat. No. 6,782,150, entitled “Apparatus for Sensing Fluid in a Pipe;” U.S. Pat. No. 6,691,584, entitled “Flow Rate Measurements Using Unsteady Pressures;” and U.S. Pat. No. 6,354,147, entitled “Fluid Parameter Measurement in Pipes Using Acoustic Pressures,” hereinafter referred to as the “flowmeter references.” However, these flowmeter references fail to provide any ability to reliably monitor sand production at the surface or downhole in real-time while other parameters are measured.
Therefore, there exists a need for a sensor that can be placed at any location along a production pipe to detect sand particles within fluid flow.